Tangle-proof electrode coil for electric discharge device



- 1965 T. A. HOFFMANN ETAL 3,218,501

TANGLE-PRCOF ELECTRODE COIL FOR ELECTRIC DISCHARGE DEVICE Filed July 26,1962 FIG. I.

PRIOR ART FIG. 5.

30 T INVENTORS.

24 28a THOMAS A. HOFFMANN &

THOMAS H. HEINE.

u. lipchd United States Patent 3,218,501 TANGLE-PROOF ELECTRODE C011.FQR ELECTRIC DISCHARGE DEVICE Thomas A. Holfmann, Morris Plains, andThomas H. Heme, Cedar Grove, N.J., assignors to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of Pennsylvania FiledJuly 26, 1962, Ser. No. 212,539 6 Claims. (Cl. 313341) This inventionrelates to discharge devices and, more specifically, to an improvedelectrode for a rapid-start fluorescent lamp.

In order to reduce the wattage dissipated in the electrodes of so-calledrapid-start fluorescent lamps during normal operation, the size of theelectrodes is reduced by decreasing the number of secondary or majorturns in the coiled coil. Since the preheating current in such lampsflows through the electrodes continuously after the lamp has beenstarted and is normally operating, the size or mass of the electrodesmust be decreased in order to keep the Wattage dissipated by theelectrodes during normal operation within acceptable limits. Suchrapidstart fluorescent lamp electrodes accordingly consist of a coiledcoil that have approximately three secondary or mapor turns and longlegs that extended axially outward from each end of the coil barrel. Theprior art rapidstart electrodes which embody this degisn are shown inFIGS. 1 to 3 of the accompanying drawing and are described in detail inU.S. Patent No. 2,774,918 issued December 18, 1956, to E. Lemmers.

The aforesaid problem does not arise in the case of conventional orso-called preheat type fluorescent lamps since the preheating current isautomatically terminated, after starting, by a glow switch or the like.

When attempts were made to reduce the manufacturing cost of suchrapid-start fluorescent lamps by automatically feeding the electrodesinto the stem-making machine, it was found that the coils had a tendencyto tangle and would not separate when placed into the hopper of anautomatic feeding unit. In such units the hopper is mechanicallyvibrated in such a manner that the coils in the hopper walk up a helicaltrack that is wide enough to hold only a single coil. The coils are,accordingly, fed one at a time from the track into a suitable transferdevice, and then into the stem-making machine.

It was found that the tangling was due to the fact that when a pair ofcoils become axially aligned the leg'of one coil would enter the shortbarrel of the other coil, and vice versa, thus causing the coils tobecome interlocked. Moreover, since the coil barrel was short and wasterminated by long legs at each end, such rapid-start electrodes wereinherently unstable when placed on a flat surface. Thus, even those thatwere not interlocked tended to wobble along the track of the feedingunit and frequently fell back into the hopper further complicating thecoil-feeding problem.

It is accordingly the general object of the present invention to providean improved electrode coil for an electric discharge device which can beautomatically handled and fed into a mounting machine.

Another and more specific object is the provision of a coiled electrodefor a rapid-start fluorescent lamp, which electrode can be automaticallytransferred into the stemmaking machine and has substantially the sameelectrical characteristics as the electrodes employed heretofore.

The aforesaid objects and other advantages are realized according tothis invention by forming an additional turn at each end of the coiledcoil, which turn is wound at a much greater pitch than the major turnswhich comprise the coil barrel. The axially extending legs are,accordingly, very short and are automatically prevented from enteringthe barrel of another coil by the open turn at the ends of the coils.The pitch of the additional open turns is such that the primary coillength and, thus, the electrical characteristics of the improved coilsare substantially the same as that of a conventional coil.

A better understanding of the invention will be obtained from theaccompanying drawing, wherein:

FIGURE 1 is a side elevational view on an enlarged scale of a prior artelectrode used in rapid-start fluorescent lamps;

FIG. 2 is a cross-sectional view, on a greatly enlarged scale, throughthe leg portion of the coil along the reference line lIII of FIG. 1;

FIG. 3 is a side elevational view of a pair of such prior artrapid-start lamp electrodes that are interlocked in the mannercharacteristic of these coils;

FIG. 4 is a side elevational view of an improved electrode embodying theinvention; and

FIG. 5 is a view corresponding to FIG. 3 illustrating the maximum degreeof entanglement which can occur with the improved electrodes of thepresent invention.

While the invention is broadly applicable to various types of electrodesand devices, it is particularly adapted for use in conjunction withcoiled-coil electrodes for rapid-start fluorescent lamps and hasaccordingly been so illustrated and will be so described.

Prior art design In FIG. 1 there is shown a conventional type electrode10 heretofore employed in fluorescent lamps designed for rapid-startoperation. As shown, the electrode 10 comprises a coiled coil ofrefractory metal wire, such as tungsten, having a short barrel or bodyportion 12 that consists of approximately three secondary or major turns14 and is terminated at each end by an axially extending substantiallystraight leg 16.

As shown more particularly in FIG. 2, the electrode 10 is formed in thewell known manner by winding a fine tungsten wire 18 around alarger-diametered tungsten core wire 20 to form a composite primarywire. This primary wire is then wound about a mandrel to form a primaryWinding or coil which is then coiled around another and much largermandrel to form a coiled coil having the desired number of major turns14 (see FIG. 1) and thus complete the electrode. The major turns arewound at a substantially uniform pitch and are, accordingly, evenlyspaced. A detailed description of the manner in which such electrodesare fabricated and the manner in which the short barrel section andrelatively long legs enable the lamp to start without the use of a highvoltage transformer are set forth in the above-mentioned US. Patent No.2,774,918 to Lemmers.

Since the length L (see FIG. 1) of the legs 16 of the prior artelectrodes 10 are much longer than the length L of the barrel section12, it frequently happens that another coil 10a becomes so aligned withthe coil that the legs of the respective coils protrude into the barrelof the other coil in the manner shown in FIG. 3. When this occurs thecoils become interlocked to such a degree that they cannot work freewhen they are placed into the vibrating hopper of the coil-feeding unitand, accordingly, are unable to ride up the feeding track. Since thelegs 16 and 16a of the respective electrodes 10 and 10a extend throughand beyond the respective coil barrels 12 and 12a and press against theinner surfaces of the major turns 14 and 14a, there is little or nofreedom of movement between the interlocked electrodes and the only wayin which they can be separated is by manually forcing them apart.

As a specific example of the dimensions of the various portions of priorart type coils, a conventional electrode designed for use in a 40-wattrapid-start fluorescent lamp generally has a coil barrel L (see FIG. 1)that is approximately 90 mils long, 60 mils in outside diameter andincludes three major turns Wound at about 33 turns per inch (TF1). Thelength L of each of the legs isapproximately 250 mils. Thus, the legsare much longer than the length of the coil barrel and easily protrudeinto and through the barrel of another coil when the coils becomeentangled in the manner shown in FIG. 3.

The invention As is shown in FIG. 4, the aforesaid coil-tangling problemis overcome according to the present invention by providing a modifiedelectrode 22 that has a coil barrel 24 with the same number of secondaryor major turns 26 as the above-described prior art electrodes but whichis terminated at each end by an open turn 28 and by a very short leg 30.The additional end or open turns 28 are Wound at a much greater pitchthan the major turns 26 so that there is a relatively large spacing pbetween the axial-extending legs and the proximate ends of the coilbarrel. By forming a portion of each of the legs into a single open turnin this manner, the legs are not only greatly reduced in length but areprevented from protruding into the coil barrel of another electrode bythe respective open turns. The improved electrodes are, accordingly,inherently tangle-proof. The pitch p of the open turns is preferablymade such that it is equivalent to about A; the length of the adjoiningleg. Expressed differently, the length of each of the legs 30 is suchthat it is approximately equal to 1% times the pitch p of the adjoiningopen turn 28.

As a specific example of the relative dimensions of the various parts ofthe improved coils, in the case of an electrode for a 40 wattrapid-start fluorescent lamp the coil barrel 24 consists of three majorturns wound at approximately 33 TPI and has a length L (see FIG. 4) ofapproximately 90 mils, as in the case of the prior art electrodesdescribed above. Each of the open turns 28 are Wound at approximately 13TPI and thus has a pitch p (or an axial length) of about 75 mils. Thisis equal to a primary coiling length of about 150 mils. Each of the legs30 have an axial length L of about 100 mils so that the length ofprimary coiling utilized in each leg and the adjoining open turn isabout 250 mils, which is equivalent to that used in each of the legs ofa conventional type electrode of the same rating. The improved electrode22, accordingly, has approximately the same primary coiling length asthe prior art electrodes and, thus substantially the same electricalcharacteristics. However, since the leg length is much shorter theoverall length of the improved coil is also somewhat shorter, as will benoted from a comparison of FIGS. 1 and 4.

As shown in FIG. 5, even if the shortened leg 30 of one electrode 22should become interlocked with the spaced end turn 28a of anotherelectrode 22a, the degree of interlock is so minor compared to thatencountered with the prior art electrodes that the coils very readilywork free by themselves when vibrated in the hopper of the coil-feedingunit. Since only the open turn of each of the coils is engaged by thelegs of the other coil, only a very small amount of relative movementbetween the electrodes will free them. Once free, the improved coils canproceed up the feeding track one at a time in the proper manner.

Moreover, the inherent instability of the prior art electrodes producedby the relatively short coil barrel and relatively long and heavy legsis also corrected by the present invention since the legs of theimproved electrodes are relatively short and the open turns at each endof the medial coiled section or barrel provide additional points ofcontact with the surface on which the electrode rests. Thus, theimproved electrodes do not wobble or tip as they proceed up thevibrating feeding track and automatically align themselves on the trackin a continuous row.

Conclusion It will be appreciated from the foregoing that the objects ofthe invention have been achieved insofar as an improved electrode for arapid-start fluorescent lamp or the like has been provided, whichelectrode is so designed that it can be shipped and handled in bulkwithout becoming tightly interlocked with other electrodes. In addition,the improved electrodes are more stable than those used heretofore andthus can readily be automatically fed along a track into a stem-makingmachine and mounted.

While one embodiment has been illustrated and described in detail, itwill be appreciated that various modifications in both the configurationand dimensions of the various portions of the electrode can be made.Without departing from the spirit and scope of the invention.

We claim as our invention:

1. An electrode for an electric discharge device comprising a refractorymetal wire coil having a medial coiled section, and an axially extendingleg at each end that is joined to said coiled section by an open turnwhich is substantially aligned with said coiled section.

2. The electrode set forth in claim 1 wherein, said medial coiledsection comprises a plurality of turns wound at substantially the samepitch, and each of said open turns has a pitch greater than the pitch ofthe turns comprising said medial coiled section.

3. The electrode set forth in claim 1 wherein the pitch of each of theopen turns is equivalent to about A the length of the adjoining leg.

4. An electrode for an electric discharge lamp comprising a coiled coilof refractory metal wire having an elongated body portion ofpredetermined length that is terminated at each end by (a) an open turnthat is aligned with said body portion and (b) a substantially straightleg that is shorter than said body portion and axially extends from saidopen turn.

5. An electrode for a fluorescent lamp comprising, a first refractorymetal wire wound into a coiled coil of linear configuration the majorturns whereof are wound, at a substantially uniform pitch, and a secondrefractory metal wire of smaller diameter Wound around said first Wire,said coiled coil being terminated at each end by an aligned open turnthat has a pitch greater than the major turns which comprise the bodyportion of said coiled coil, and by a leg that extends axially beyondsaid open turn for a distance approximately equal to 1 /3 times thepitch thereof.

6. An electrode for a rapid-start fluorescent lamp comprising, a firstrefractory metal wire wound into a coiled coil of linear configurationhaving no more than four major turns that are Wound at a substantiallyuniform pitch, and a second refractory metal wire of smaller diameterwound around said first wire at a substantially uniform pitch, saidcoiled coil being terminated at each end by an aligned open turn thathas a pitch greater than the major turns which comprise the body portionof said coil, and by a leg that extends axially from and beyond saidopen turn for a distance approximately equal to 1 /3 times the pitchthereof.

1. AN ELECTRODE FOR AN ELECTRIC DISCHARGE DEVICE COMPRISING A REFRACTORYMETAL WIRE COIL HAVING A MEDIAL COILED SECTION, AND AN AXIALLY EXTENDINGLEG AT EACH END THAT IS JOINED TO SAID COILED SECTION BY AN OPEN TURNWHICH IS SUBSTANTIALLY ALIGNED WITH SAID COILED SECTION.